Follow your heart. I think the general rule to follow is: If you love your BF you must forget about your ex. If you love your ex you must forget about your boyfriend. If you don't love either of them, it doesn't really matter what you do. If you want to break up and stay friends with your boyfriend you need to talk to him about your feelings. Its probably a good idea to give him atleast a few months after you break up before you resume a relationship with your ex, or a friendship with him. That is for his sanity. If you want to stay in your relationship and be friends with your ex, tell your ex that you are not interested in having a relationship with him any more. You need to be firm in this regard.

girls need the perspective from a guy that is actually in the situation, my ex gf had a bf for 3 years and started loving him around a year and a half but the last year he had been more of a friend than anything else not interested in her or didn't care to try, they finally broke up and she decided to try something with me, i belive it or not have been nothing but good to her, i have made sure that anything she wants or needs she has, never once have i chose friends over her, and i even took her on vacation when she said she needed one no questions asked, she said i had treated her better than anyone in her life, and she started loving me or so she says, but a few days ago he asked her to go back because now he realized what he had, all this because he saw i was with her now, i love her and i know it and the hardest thing for me to do was let her go even though she never asked, i just want her to be happy, but she wants to try getting back with him without loosing me, i decided to stick around just as a friend but its killing me, but im willing to stay around. truth is when a guy really cares he will do anything, anytime for the rest of his life, so if you feel he isn't carying anymore give your self a shot you wont know if another guy will do things like my self unless you try, and if the other guy turns out to be a jerk, dump his ass and look for another one, there is millions of them and there is good ones still, you just have to recognize them, and when you get that one that is willing to be there for you dont ever dought in him and loose him because you feel what you had once will ever come back, once the spark is gone there is nothing left.